Process for pretreating mixed hydrocarbon dealkylation stock

ABSTRACT

A hydrocarbon liquid stream is conditioned for hydrodealkylation by first fractionating the stream to obtain a heart-cut containing aromatics, and substituted aromatics and paraffinic hydrocarbons of similar boiling points. The heart-cut is then contacted in the presence of a suitable catalyst with a gas comprising a mixture of hydrogen and carbon dioxide, hydrogen and carbon monoxide. The resultant product is fractionated into a hydrodealkylation feed stream low in those paraffinic hydrocarbons which crack and consume hydrogen during the hydrodealkylation of alkyl-substituted aromatics and rich in compound having a molecular weight greater than napthalene.

Elite States Patent [191 Green et al.

451 Dec. 17,1974

[54] PROCESS FOR PRETREATING MIXED 2,774,801 12/1956 Coonradt et a1.260/672 R HYDROCARBON DEALKYLATION S O 2,958,643 11/1960 Friedman3,197,524 7/1965 Backlund 260/672 R [75] Inventors: William S. Green,Columbus; John Newman Ashland both of Primary Examinerl-lerbert Levine73] Assignee: Ashland Oil, Inc., Ashland, Ky. Attorney, Agent, orFirm-Van D. Harrison, Jr. [22] Filed: Apr. 27, 1973 211 App]. No.:355,089 [57] ABSTRACT Rdated Application Data A hydrocarbon liquidstream is conditioned for hydro- [63] Continuation an of s r N '63 845 Jl 19 dealkylation by first fractionating the stream to obtain 1971abando'ne: e u y a heart-cut containing aromatics, and substituted aromatics and paraffinic hydrocarbons of similar boiling [52] us Cl 208/121208/59 208/] 12 points. The heart-cut is then contacted in the presence36 268/123 560/672 of a suitable catalyst with a gas comprising amixture [51] Int Cl i 11/04 C10g 13/04 of hydrogen and carbon dioxide,hydrogen and carbon [58] Fieid 260/672 2O8/59 123 monoxide. Theresultant product is fractionated into a 208/121 1 hydrodealkylationfeed stream low in those paraffinic hydrocarbons which crack and consumehydrogen [56] References Cited during the hydrodealkylation ofalkyl-substituted aromatics and rich in compound having a molecularUNITED STATES PATENTS weight greater than napthalene. 2,653,176 9/1953Beckberger 260/672 R 2,734,929 2/1956 Doumani 260/672 R 4 Claims, 1Drawing Figure LIGHT GASOLINE 36-7. 16 -S GASOLINE l *2 FUEL OIL 25 34CRACKED PRODUCT 20 2e 38 FROM Fcc UNIT 7 Y K J CYCLE HEART on. cm

SLURRY OIL l za PITCH FRACTION H2 co on CO2 PROCESS FOR PRETREATINGMIXED I-IYDROCARBON DEALKYLATION STOCK CROSS REFERENCES TO RELATEDAPPLICATIONS This application is a continuation-in-part of our copendingapplication Ser. No. 163,845 filed July 19, 1971 now abandoned.

NATURE OF THE INVENTION The present invention relates to a method forpreconditioning or pretreating a liquid hydrocarbon stream whichsubsequently is to be the feedstock for hydrodealkylation and relatesalso to the hydrocarbon product so preconditioned or pretreated.

PRIOR ART In the prior art, it has been well known to obtain mononuclearand polynuclear aromatic hydrocarbons from various sources. One suchsource of aromatics is a coal tar fraction. The coal tar fractioncontains some aromatics which are unsubstituted and, therefore, usefulas such, and substituted aromatics having substituent groups, such asmethyl and ethyl groups. It is also known that the alkyl substitutedaromatics may be dealkylated to improve the product yield. Other sourcesof aromatics, in addition to coal tar distillates, include tar sands,shale oil, bone oils, wood tar and other naturally occurring materials.Still another source of aromatics are the various products resultingfrom processes for refining liquid petroleum oil. Since liquid petroleumoils are basically made up of the same components as tar sands, shaleoils and the like, except for relative quantities of components and theform of crude products, large amounts of aromatics occur in petroleumoils, depending upon their origin, and as a result large amounts ofimpure aromatics and aromatic precursors are obtained as products ofvarious processes for refining petroleum oil to produce the usualultimate product gasoline. Most refinery streams containing substantialamounts of aromatics are, of course, impure streams and the aromaticsmust be separated from paraffinic, naphthenic and other types ofhydrocarbons. One method of making this separation involves the use ofaromatic selective solvents such as furfural and the like. Suchselective solvents, however, also separate alkylated aromatics, whichwere previously referred to as aromatic precursors. As is the case withcoal tar distillate fractions, the alkylated aromatics in petroleum oilstreams include both mononuclear and polynuclear alkyl substituentmaterials. In addition, the substituent groups include one or moremethyl groups, ethyl groups and the like. Accordingly, in order toproduce aromatics in commercial yields it is necessary to convert thealkylated aromatics to unsubstituted products. This conversion isgenerally carried out by dealkylating the substituted aromaticsgenerally by what is known as a hydrodealkylation operation. In suchhydrodealkylation methods the feedstock is treated at high temperatureswith hydrogen or hydrogenproducing compounds in the presence of acatalyst in order to selectively split off the alkyl group or groups.This process is especially well suited for the dealkylation ofmononuclear and binuclear aromatics. Such hydrodealkylation operationsmay be carried out at temperatures between 800 and l,500F. Higher yieldscan generally be obtained by operating at or near the upper temperaturelimits. These upper temperature limits are also advantageous whenoperating on comparatively high boiling feedstock materials. The majordifficulty, however, in all hydrodealkylation processes, even at lowtemperatures, is in the formation of carbon and coke during thereaction. The carbon and coke formation is considered to result, atleast in part, from the cracking of paraffinic hydrocarbons present inthe hydrocarbon stream being subjected to hydrodealkylation. Becausesome of the paraffinic hydrocarbons have boiling points in the samerange as those of the alkyl substituted aromatics to be treated in ahydrodealkylation process, fractionation of mixtures of aromatics,alkyl-substituted aromatics and paraffinic hydrocarbons will remove onlythose paraffins of lower boiling point ranges. The formation of tar andcoke in the hydrodealkylation process results in a rapid plugging anddeactivation of the catalyst and the frequent necessity of shutting downthe operation to clear the catalyst and regenerator. This frequent andtime-consuming shut down, clean up, and regeneration obviously resultsin an expensive and a highly inefficient overall operation.

The presence of paraffins in hydrocarbon mixtures being subjected tohydrodealkylation also contributes to the excessive consumption ofhydrogen gas required in the process. A number of years ago hydrogen gaswas a refinery byproduct in excess supply and its cost was not a majorfactor in the cost of hydrodealkylating. Now, however, the need forhydrogen gas in other refining processes such as sulfur removal andisomerization has increased the demand for hydrogen to such an extentthat often it must be specifically manufactured from natural gas forrefining uses. During the hydrodealkylation of hydrocarbon mixtures theextreme conditions prevailing result in excessive cracking of theparaffinic hydrocarbons. The cracked hydrocarbons in turn, because theycontain reactive carbon atoms, react with hydrogen gas present in thehydrodealkylation process. Consequently the excessive cracking ofparaffin hydrocarbons in the hydrodealkylation process results inexcessive consumption of hydrogen gas.

OBJECT OF THE INVENTION It is, therefore, an object of the presentinvention to provide a method for pretreating a hydrodealkylationfeedstock. Another object of the present invention is to provide animproved technique for the preparation of a hydrodealkylation feedstockfrom high boiling catalytic cracking products. Yet another object of thepresent invention is to provide an improved technique for thepreparation of a hydrodealkylation feedstock from a catalyticallycracked slurry oil, a catalytically cracked cycle oil and mixturesthereof.

Still another object of this invention is to provide a method whereby afeedstock to be hydrodealkylated may be preconditioned or pretreated sothat excessive quantities of hydrogen will not be consumed during thehydrodealkylation process by reaction of cracked paraffins with hydrogengas present.

Still another object of this invention is to provide a method wherebythe paraffins present in a mixture of paraffins, aromatics, and alkylsubstituted aromatics, all of which have similar boiling points, may bemildly cracked and hydrogenated to paraffins having boiling points lowerthan the associated aromatics and alkyl substituted aromatics.

SUMMARY OF THE INVENTION Briefly stated, our invention comprises amethod whereby a hydrocarbon stream containing paraffins, aromatic, andsubstituted aromatic compounds is fractionated to provide a heart-cutfraction containing a concentration of aromatic, substituted aromaticcompounds and substantial amounts of paraffins which is then contactedwith a gas mixture of carbon oxide gases and hydrogen-containing gasesover a suitable hydrocracking catalyst. In still another embodimentcarbon dioxide alone is contacted with the heart-cut fraction over asuitable catalyst.

BRIEF DESCRIPTION OF THE DRAWING The accompanying Drawing is a flowsheet depicting our invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Our invention is applicable toany hydrocarbon product of petroleum or coal tar origin containingsignificant amounts of paraffins together with aromatics, specificallymononuclear and polynuclear aromatic compounds having substituent alkylgroups and particularly the higher boiling mononuclear and polynuclearmaterials.

One source of mixtures of these materials is product streams from thecracking of petroleum hydrocarbons. Such cracking yields large amountsof mixtures of aromatics, alkyl substituted aromatics and paraffins.While such mixtures may be utilized in motor fuels and other products assuch, greater demand for these products exist in the pure chemical fieldwhere highly purified materials are desired for use as solvents andchemical intermediates. By way of specific example, product streamsobtained by fractionating the liquid product of a fluid catalyticcracking process, produce feedstocks which benefit most significantly bythe use of the present treatment.

Referring now to the drawing, a cracked product from a fluid catalyticcracking unit is fed to fractionator 10 through line 12. In fractionator10, the fluid catalytic cracking product is separated into a lightgasoline fraction which is discharged through line 14, a gasolineproduct discharged through line 16 and a No. 2 fuel oil productdischarged through line 18. These three materials, of course, havedirect uses in industry and further reference thereto is unnecessary. Inaddition to the above, the remaining or bottoms of the fractionatingoperation is split into what is called a cycle oil normally having aboiling point of about 400 to 700F and a higher boiling slurry oilnormally having a boiling range of about 650 to l,000F. The cycle oil isdischarged from fractionator 10 through line 20 and the slurry oilthrough line 22. Both of these materials are rich in alkyl aromatics andby the same token because of their high boiling point also containsubstantial amounts of paraffins. Preferably, the slurry oil isclarified as by settling, distillation, or other means after it leavesfractionator l and before it is treated further. However, thisconventional operation is not shown so that the drawing will not beunduly complicated.

The slurry oil and/or the cycle oil are fed to fractionator 21 whereeither (or a mixture of the two) is fractionated to provide a heart-cutfraction boiling between about 400 to 575F. Preferably, a fractionboiling between 400 and 515F. is used. The heart-cut fraction soobtained contains quantities of aromatics and alkyl substitutedaromatics, but although free of the lowerboiling point paraffins andnaphthenes, this fraction still contains paraffins having boiling pointsof or near the boiling point of the desired aromatics. From fractionator21, the heavier fraction or higher boiling pitch fraction is dischargedthrough line 23 and the overhead fraction is discharged through line 24.The heart-cut fraction after leaving fractionator 21 and before enteringline 26 can, if desired, be desulfurized by known techniques. Thisdesulfurization is a conventional and well-known process to thoseskilled in the art and for this reason is not specifically illustratedin the drawing.

In line 26 the heart-cut fraction is mixed with hydrogen and a carbonoxide gas (or with carbon dioxide alone) and is then passed to reactor25 by way of line 26. Hydrogen is injected into line 26 through line 28and at the same time, a carbon oxide gas, either carbon dioxide orcarbon monoxide, is injected into line 26 through line 30. In stillanother alternative, carbon dioxide alone is injected into line 26 bymeans of line 30, that is, no hydrogen is added to the system from anextraneous source. A mixture of hydrogen, carbon oxide gas and heart-cutfractions, or alternatively carbon dioxide and heart-cut fraction flowsthrough line 27 into reactor 25.

The reactor 25 may be any conventional apparatus adapted for contactinggases and liquids in the presence of a solid catalyst. For example,fixed, circulating and fluid bed contactors having single or multiplebeds may be employed. Such contactors may be operated according tovarious modes such as batch, cyclical or continuous. In a continuousoperation, the heart-cut liquid is contacted countercurrently orconcurrently with gases introduced into the reactor in the presence ofthe solid catalyst. Heat may be supplied by suitable preheating of thecatalyst or by internal or external heating of the reactor itself and/orby preheating the feed fluids. Contact time and heat supplied may beregulated by suitably adjusting the flow rate of catalyst and feedmaterials. In a cyclic operation, a plurality of stationary beds ofcatalysts are ordinarily employed wherein some of the units may bemaintained on stream at all times while others are undergoingregeneration or cleaning. Heat ordinarily is supplied externally or byinternal heating elements and the operation may be conducted atatmospheric pressure or above. In accordance with the preferredembodiment of the invention, a fixed bed reactor unit is employed. Freshor regenerated catalyst is held stationary in the reactor and the feedis passed downwardly through the bed under pressure on a continuousbasis. If coke or carbon build up in the bed, the pressure drop acrossthe bed increases. When the pressure drop and carbon content of the bedreach levels which are either inconvenient or impossible to work with,the bed is no longer usable and the reactor is shut down. Then thecatalyst is either regenerated in the reactor or is removed and replacedwith fresh catalyst. Under the mild operating temperatures theparaffinic hydrocarbons present are only mildly cracked and hydrogenatedto a point where their boiling points are substantially lower than theboiling points of the aromatics and alkyl substituted aromatics present.Because the mild operating temperatures used minimize the production ofcarbon in the catalyst bed, only infrequent shut downs on account ofcarbon formation in the catalyst bed are necessitated and do notconstitute a serious interruption of production.

In operation of the reactor or treating unit 25, temperatures of betweenabout 500 to 1,150F. can be employed although about 900 to 1,100F. ispreferred. A weight-hourly space velocity between about 0.25 and 2.5 canbe employed, although about 0.8 to 1.5 is preferred. The pressureutilized may also vary over a wide range from about 250 to 2,000 psi.However, the preferred operating pressure is between about 400 and 1,000psi. The hydrogen to feedstock mol. ratio may range from about 1 to 50but is'preferably from about 2.5 to 25. correspondingly, the carbonoxide to feedstock mol. ratio may range from about 0.1 to 50 but ispreferably from about 0.25 to 25.

As for the catalyst used in reactor 25, it has been found that acatalyst having nickel oxide as an active ingredient is best suited foruse where the hydrocarbon stream is to be contacted with a mixture ofcarbon oxide and hydrogen, or carbon dioxide by itself. A catalystmeeting this description is one manufactured by the American CyanamidCompany under the trade name of AERO I-IDS-3 and AERO HDS-BA. These areextruded nickel-molybdena catalysts on an alumina base and have typicalpropertles shown in Table I.

TABLE I COMPOSITION (WT. AERO l-IDS-3 AERO I-IDS-3A NiO 3.2 3.2 MoO 15.115.1 Na O 0.02 0.02 Fe 0.04 0.04 80.. 0.3 0.3 SiO 0.1 0.1 Loss onignition 1.4 1.4

PHYSICAL PROPERTIES Apparent bulk density (lbs/ft) 40 40 Comgacted bulkdensity (lbs/ 43 43 Average diameter (in) 0.13 0.07 Average length (in)0.22 0.18 Average crush strength (lbs) l7 15 Loss on abrasion (wt%) 0.40.4 Pore volume 0.6 0.6 Surface area (m fg) 180 180 Through No. 7 mesh(wt%) 0.2 0.2 Through No. 14 mesh (wt%) *ACI'IVITY sulfur removal atSLHSV 93 94 at IOLHSV 82 84 nitro en removal at L SV 70 75 at IOLHSV 5055 Standard conditions 01' 705F., 750 psig. 2500 scf/bbl H, rate. Texasgas oil of 33.5AP| and 1.2 wt. '1 sulfur. LHSV liquid hourly spacevelocity, or volume of l'eed/hrJvolume of catalyst LI-ISV liquid hourlyspace velocity, or volume of feed/hr./volume of catalyst Anothersuitable catalyst is a cobalt-molybdenum catalyst. A typicalcobalt-molybdenum catalyst is marketed under the trade name Nalco 471 bythe Nalco Chemical Company. Another suitable catalyst is marketed byHarshaw Chemical Company under the trade name ZN-0308T. This catalystcomprises zinc chromite and has a typical composition of 74% zinc oxideand 22 to 23% chrome oxide.

After passage through reactor 25 the feedstock is passed through line 32to fractionator 34. In fractionator 34 any high boiling condensed andpolymerized paraffins present are separated, but more importantly thenewly formed cracked and hydrogenated paraffins now having substantiallyreduced boiling points are removed. The overhead fraction is dischargedthrough line 36 and the higher boiling materials, those boiling aboveabout 550F. are discharged through line 40. The principal and desiredfraction containing most of the monoor polycyclic material boiling fromabout 400 to 550F. or more desirably between about 425 and 500F. isremoved through line 38. This is the hydrodealkylation feedstock nowdepleted in paraffin content which is then subjected to conventionalhydrodealkylation treatment. The step of hydrodealkylation does not forma part of our invention and is a process well known to those skilled inthe art. Accordingly, it is not discussed further here.Hydrodealkylation is described in a number of patents, for example US.Pat. No. 3,075,022.

The following examples illustrate the outstanding results which havebeen obtained in accordance with our invention.

EXAMPLE 1 A light cycle oil from a fluid catalytic cracking unit wasfractionated to provide a heart-cut having a boiling point range of 400to 515F. Seven separate portions of this fraction were contacted with anickel molybdenum catalyst and a cobalt molybdenum catalyst as shown inTable II in the presence of carbon dioxide and hydrogen injected at theflow rate shown in Table II. Other conditions of contact are also shownin Table II. As shown in Table II, the percentage of material having amolecular weight less than that of the alkyl naphtha lene was increasedfrom 2.8 in the feedstock to between 26 and 42%. The amount of materialhaving a molecular weight greater than that of methyl naphthalene wassubstantially decreased.

The data in Table II shows that feedstock to the hydrodealkylationprocess can be preconditioned or pretreated successfully in a mixedhydrogen-carbon dioxide atmosphere. Either the Nalco 471 or l-IDS-3Acatalyst will achieve the pretreatment level desired.

TABLE II TREATMENT OF UIOI-IC IN A CO -H (25%COJ75%H ATMOSPHERE Test48-5-1 48-5-2 48-7-1 48-7-2 48-1 1-1 48-1 1-2 48-51-] Catal st HDS-3Al-IDS-3A l-IDS-3A EDS-3A N-471 N-471 HDS3A Feed l-"(ate of Heart-cutlight cycle oil (Wl-ISV) 1 1 1 1 1.1 1 0.9 Gas Rate In (SCF/l-I) 1.9 1.91.9 1.9 1.65 1.65 1.20 Gas Rate Out (SCF/l-I) 1.67 1.65 1.68 1.73 1.421.66 0.79 Pressure (PSIG) 400 400 400 400 400 1000 1000 Avera e Bed Tem(F.) 933 983 1033 1084 983 984 985 LiquicFYield (Wt. 11) 89.5 71.3 70.267.7 82.7 75.3 79.1

TABLE II Continued TREATMENT OF LCOHC IN A CO -H (25%CO /75%H ATMOSPHERETest 48-5-1 48-5-2 48-7-1 48-7-2 48-1 l-l 48-1 1-2 48-51-1 Weight PerCent Product Analysis Feed Molecular wt. less than naphthalene 2.8 26.133.3 34.4 31.3 29.5 42.0 37.2 Naphthalene 1.4 5.6 6.9 8.0 5.2 5.9 10.48.0 Molecular wt. between na hthalene & meth naphthalene 4.7 6.0 5.5 4.89.6 3.4 5.8 4.6 Methyl aphthulcnc 18.7 20.1 21.5 21.6 18.3 26.6 20.9 209Molecular wt. greater than naphthalene 72.0 42.2 g 32.8 31.2 35.6 34.620.9 29.3

EXAMPLE 2 EXAMPLE 3 Additional samples of light cycle oil having thesame boiling point range as that of Example 1 was contacted with nickelmolybdenum and zinc chromite catalysts and a synthesis or water gascomprising: two-thirds hydrogen gas and one-third carbon monoxide gas.The amount of material converted into the lighter than naphthalene rangewas again substantially increased to Additional samples of the heart-cutfraction of Example l were contacted in a pure carbon dioxide atmo- 20sphere with nickel molybdenum and zinc chromite catalysts as shown inTable IV. Again the percentage of material having a molecular weightless than the alkyl naphthalenes was substantially increased.

While specific examples have been given herein and percentages of fromabout 22 to about 36%. The result 25 specific illustrations set forth,it is to be recognized that of these series is shown in Table 111.

these recitals are made only in an effort to teach those TABLE 111TREATMENT OF LCOHC IN A SYNTllESlS GAS ATMOSPHERE Test 21-195-1 21-195-248-3-1 44-41-1 44-41-2 44-41-3 Catal st HUS-3A HDS-3A HDS-3A Zn-0308TZn-0308T Zn-0308T Feed ate (WHSV) 0.99 1.01 0.97 0.96 0.99 0.86

Gas Rate ln (SCF/H) 1.9 1.9 1.9 4.1 4.1 4.1

Gas Rate Out (SCF/H) 1.66 1.83 1.30 3.38 3.60 2.33

Pressure (PSlG) 400 400 Average Bed Temp. (F.) 984 1035 1084 985 10351078 Li uld Yield Product Analysis Weight Per Cent Molecular wt lessthan naphthalene 36.2 35.1 32.5 22.0 23.4 30.3

Naphthalene 6.8 7.3 5.3 4.2 4.7 4.2

Molecular wt.

between naphthalene and methyl naphthalene 5.0 4.8 3.6 4.9 4.5 4.7

Methyl naph. 19.7 20.5 20.4 19.7 19.8 185 Molecular wt.

heavier than methyl naph. 32.7 32.3 38.3 49.2 47.5 42.3

TABLE IV PARTlAL DEALKYLATION OF LCOHC IN A CO ATMOSPHERE Test 21-191-121-191-2 4435-1 4437-1 4437-2 Catalyst HDS-3A HDS-3A Zn-0308 ZN-0308Zn-0308 Feed Rate (WHSV) 1.0 1.0 1.01 1.01 0.99 Gas Rate 1n (SCF/l-l)1.9 1.9 4.1 4.1 4.1 Gas Rate Out (SCF/l-l) 1.93 1.76 4.03 4.15 4.45Pressure (PSlG) 600 400 400 400 400 Avera e Bed Tmp. (F.) 983 983 1036983 1034 1083 Liqui Yield (Wt. 89.2 65.2 97.2 89.2 78.4

Product Analysis Feed Weight Percent Molecular wt. less than naphthalene2.8 18.4 28.1 9.2 17.0 26 1 Naphthalene 1.4 2.3 2.8 1.1 1.6 2 1 TABLElV-Continued PARTIAL DEALKYLATION OF bCOHC IN A CO ATMOSPl-lERE Test21-191-1 21-191-2 44-35-1 44-37-1 44-37-2 Molecular wei t between naphalene & methyl naphthalene 4.7 5.4 4.2 6.3 5.5 3.0 Methyl naphthalene18.7 17.1 17.2 17.4 17.0 18.4 Molecular weight greater than methylnaphthalene 72.4 56.8 47.7 66.0 7 13,9 50.4

skilled in the art a preferred operation in accordance on alumina, andZinc chromite; and with the present invention. Accordingly, it is to beunb f ti ti h li id r duct obtained from (a) derstood that the presentinvention is to be limited only i t a f ti b ili g between about 400F.and

by the appended claims.

What we claim is:

1. A process for preparing a hydrocarbon mixture containing paraffinic,aromatic and alkyl substituted aromatic hydrocarbons for subsequenthydrodealkylation, said mixture having a boiling point of between about400F. and about 550F. comprising:

a. contacting said hydrocarbonmixture with a gas consisting of carbondioxide in the absence of hydrogen added from sources extraneous to saidprocess and in the presence of a catalyst selected from the groupconsisting of nickel oxide and molybdena about 550F., thereby providinga suitable hydrodealkylation feedstock.

2. The process of claim 1 wherein said catalyst of (a) consistsessentially of zinc chromite.

3. The process of claim 1 wherein said catalyst comprises nickel oxideand molybdena on alumina.

4. The process of claim 1 wherein said hydrocarbon mixture having aboiling point of between about 400F. and about 550F. is a fraction of acycle oil having a boiling point of about 400F. to about 1,000F.

1. A PROCESS FOR PREPARING A HYDROCARBON MIXTURE CONTAINING PARAFFINIC,AROMATIC AND ALKYL SUBSTITUTED AROMATIC HYDROCARBONS FOR SUBSEQUENTHYDRODEALKYLATION, SAID MIXTURE HAVING A BOILING POINT OF BETWEEN 400*F.AND ABOUT 550*F. COMPRISING: A. CONTACTING SAID HYDROCARBON MIXTURE WITHA GAS CONSISTING OF ACCARBON DIOXIDE IN THE ABSENCE OF HYDROGEN ADDEDFROM SOURCES EXTRANEOUS TO SAID PROCESS AND IN THE PRESENCE OF ACATALYST SELECTED FROM THE GROUP CONSISTING OF NICKEL OXIDE ANDMOLYBDENA ON ALUMINA, AND ZINC CHROMITE; AND B. FRACTIONATING THE LIQUIDPRODUCT OBTAINED FROM (A) INTO A FRACTION BOILING BETWEEN ABOUT 400*F.AND ABOUT 550*F., THEREBY PROVIDING A SUITABLE HYDRODEALKYLATIONFEEDSTOCK.
 2. The process of claim 1 wherein said catalyst of (a)consists essentially of zinc chromite.
 3. The process of claim 1 whereinsaid catalyst comprises nickel oxide and molybdena on alumina.
 4. Theprocess of claim 1 wherein said hydrocarbon mixture having a boilingpoint of between about 400*F. and about 550*F. is a fraction of a cycleoil having a boiling point of about 400*F. to about 1,000*F.